.Net: Update classes so namespaces are consistent and match project location

[markwallace-microsoft]

Motivation and Context

Description

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[RogerBarreto]

Thanks for:

• Splitting the ServiceCollection in it's own class, the other connectors are doing in the same, this is a good move.
• Making internal the missing request/response Models, missed that.

REgarding the namespace change I don't fully agree, as this defeats the purpose of having specific modality namespaces where classes that could be in it are all mixed in Core.